Refrigeration apparatus with compressors in parallel



- June 4, 19

68 R. J. HACKBART' 'ETAL 3,386,262

REFRIGERATION APPARATUS WITH COMPRESSORS IN PARALLEL Filed Oct. 31, 1966INVENTOR REUBEN J. HACKBART BY DUANE F. SANBORN ATTORN'EY United StatesPatent 3,386,262 REFRIGERATION APPARATUS WITH COMPRESSORS IN PARALLELReuben J. Hackbart and Duane F. Sanborn, La Crosse, Wis., assignors toThe Trane Company, La Crosse, Wis., a corporation of Wisconsin FiledOct. 31, 1966, Ser. No. 590,744 9 Claims. (Cl. 62-469) ABSTRACT OF THEDISCLOSURE A refrigeration system having parallel circuited compressorsin which means is provided for maintaining the oil Sump of onecompressor at a higher pressure than the oil sump of the othercompressor so that excess oil in the one compressor may fiow through anoil equalizer conduit to the other compressor; and means for directing agreater portion of the oil returned from the evaporator to the higherpressure oil sump.

This invention relates to refrigeration apparatus of the compressioncycle type using a plurality of compressors arranged in parallel in aclosed refrigerant circuit. More particularly this invention relates tothe problem of maintaining sufiicient oil in each of the compressors.

In a refrigeration system using a compressor, it is well known that asmall portion of the lubricating oil for the compression mechanismbecomes entrained with the refrigerant gas discharged from hecompressor. If the amount of such oil entrained in the gas is relativelysmall so as not to materially reduce the heat transfer at the condenserand evaporator, no specific problem is created if a single compressor isused as the oil will pass through the evaporator and be returned to thecompressor via the suction line. However, if two or more compressors areused and arranged in parallel in the refrigerant circuit, the oilleaving the evaporator outlet may be returned unequally to thecompressors thus starving one or more of the compressors of thenecessary lubrication required for long life. Many attempts have beenmade to solve this oil equalization problem, most of which rely uponsuch schemes as pumping oil from one compressor to the other orequalizing the crankcase or oil sump pressures. It is difficult touniformly obtain equal pressures in the crankcases or oil sumps from oneinstallation to another and the use of an oil pump even of the ejectortype may be very costly.

Such systems are inherently complicated and/or difcult to controlresulting in a more expensive device, the cost of which must be passedon to the customer public.

It is thus an object of the instant invention to provide a refrigerationsystem using parallel compressors which is low in cost, reliable anduniformly controlled for maintaining adequate lubricating oil in eachcompressor enhancing the life of the compressors.

A further object of the instant invention is to provide a refrigerationcircuit for parallel compressors which does not depend upon theequalization of crankcase or oil sump pressures.

Another object is to provide a refrigeration circuit for parallelcompressors which requires no special oil pumping means for maintainingadequate lubricating oil in each of the compressors.

Still another object of this invention is to provide a refrigerationcircuit apparatus for parallel compressors which requires no specialcheck valves to obtain adequate lubrication in each of the compressors.

The instant invention specifically involves refrigeration apparatuscomprising a refrigerant condenser means; a refrigerant evaporatormeans; first conduit means connecting the outlet of said refrigerantcondenser means to the inlet of said refrigerant evaporator means; firstand second refrigerant compressors; a first oil sump for said firstrefrigerant compressor; a second oil sump for said second refrigerantcompressor; a first suction conduit connected to the inlet of said firstrefrigerant compressor and disposed in fluid communication with theoutlet of said refrigerant evaporator means for conducting refrigerantfrom said refrigerant evaporator means to said first refrigerantcompressor; a second suction conduit connected to the inlet of saidsecond refrigerant compressor and disposed in fluid communication withthe outlet of said refrigerant evaporator means for conductingrefrigerant from said refrigerant evaporator means to said secondrefrigerant compressor; a discharge conduit means connecting the outletsof said first and second refrigerant compressors to the inlet of saidrefrigerant condenser means for conducting refrigerant from said firstand second refrigerant compressors to said refrigerant condenser means;an oil equalizer conduit connecting said first oil sump to said secondoil sump; means for operating said first and second refrigerantcompressors simultaneously; means for maintaining the pressure in saidfirst oil sump higher than the pressure in said second oil sump duringsimultaneous operation of said first and second compressors wherebyexcess oil in said first oil sump will flow through said oil equalizerconduit to said second oil sump; and means for returning a major portionof any oil entrained in the refrigerant leaving said evaporator means tosaid first oil sump.

Other objects and advantages will become apparent as the specificationproceeds to describe this invention with reference to the accompanyingdrawing schematically showing a refrigeration system employing twohermetically sealed reciprocating refrigerant compressors arranged inparallel relation.

Now referring to the sole drawing, a refrigeration system It) forcooling a conditioned space 12 is shown having a refrigerant condenser14, a refrigerant receiver 16, a refrigerant throttling means such asthermal responsive expansion valve 18, a refrigerant evaporator 20disposed in heat exchange relation with conditioned space 12, and arefrigerant compression mechanism 22 serially arranged in a closedrefrigerant circuit.

Compression mechanism 22 includes a first compressor 24 and a secondcompressor 26. Compressors 24 and 26 may be identical and a descriptionof one will suflice for both. Compressor 24 has a hermetic casing 28.Disposed within casing 28 is a motor-compressor unit 30 which includes amotor portion 32 for driving a compress-or portion 34. Motor-compressorunit 30 is resiliently mounted within casing 28 via a centrally locatedupper spring 36 and a plurality of circumferentially spaced lowersprings 38. The lower portion of casin 28 is filled with lubricating oilthereby defining an oil sump 40. Compressor portion 34 may include anoil pumping mechanism 42 which extends into the oil sump 40 forwithdrawing oil therefrom and lubricating the mechanism of thecompressor portion. It will be understood that substantially all suchcompressing mechanism inherently entrain small amounts of lubricatingoil with the refrigerant gas being compressed. Compressor 24 furtherincludes a suction inlet opening 44 in casing 28. Refrigerant gas withincasing 28 is drawn into the motor-compressor unit through an opening 46which is preferably at the motor portion end. Compressed gas isdischarged from the motor-compressor unit at 48 from whence it passesthrough a resilient discharge tube 50 which extends through casing 28 asthe compressor discharge outlet 52.

An oil level equalizer conduit 54 communicates and connects the casings28 of compressors 24 and 26 at the desired gas-oil interface in oilsumps 40. Since this invention contemplates a difference between thesuction pressures in the casings 28 of compressors 24 and 26, it will beappreciated that oil equalizer conduit 54 will also conduct a flow ofrefrigerant gas. Adjacent the inlet to conduit 54 the gas velocity maybe sufficiently high so as to carry along oil at the gas-oil interface.To abate this type of oil transfer, a baffle plate 56 may be placed ineach casing 28 in spaced alignment with the ends of conduit 54.

Compressors 24 and 26 are connected in parallel in the refrigerantcircuit in the following manner. Each of the compressor dischargeoutlets is connected to a discharge conduit 58 and each of conduits 58communicates with the inlet of condenser 14. On the suction side ofcompressor mechanism 22 is a T- or Y-shaped conduit connector 60 havingan inlet 62 connected to the outlet of evaporator 20, a first outlet 64disposed in substantial flow alignment with inlet 62 and connected to afirst suction conduit 66 which connects to the suction inlet 44 of firstcompressor 24. Connector 60 has a second outlet 68 which issubstantially out of flow alignment with inlet 62. Outlet 68 isconnected to a second suction conduit 70 which connects to the suctioninlet of a second compressor 26. Conduit 70 is crimped at 72 to providewithin the conduit a desired flow resistance for reasons hereinafterdescribed. Connector 60 may be similar in configuration to the branchcoupling shown in US. Patent 24,179.

It will be observed that outlet 68 makes an acute angle with inlet 62while outlet 64 makes an obtuse angle with outlet 68. Stated anotherway, outlet 64 makes a larger angle with inlet 62 than the angle betweenoutlet 68 and inlet 62. It will be evident from this structure that theinertia of oil entrained within suction gas leaving evaporator 20 willcause a major portion of the oil to pass through the outlet 64 ofconnector 60 through suction conduit '66 into the casing 28 ofcompressor 24 where it may settle into the oil sump 40 of compressor 24.For the same reasons a slightly greater amount of refrigerant gas shouldpass from outlet 64 than from outlet 68 thereby maintaining a highersuction pressure in compressor 24 than compressor 26. To adjust orincrease this pressure differential suction conduit 70 is crimped at 72a desired amount as aforementioned.

The motor portions 32 of compressors 24 and 26 may be connected inparallel to a source 74 of electric power through a thermostat 76disposed to respond to the tem perature of the conditioned space 12 forsimultaneous operation of the compressors. Should it be desired to use atwo-stage thermostat to sequentially operate first one and then bothcompressors, compressors 24 having the normally higher suction pressureshould be selected as the compresor which is operated alone for lowcapacity cooling.

Operation As the temperature in the conditioned space 12 rises to apredetermined level, thermostat 76 closes the circuit for conductingelectric current from power source 74 to each of the motors ofcompressors 24 and 26 for operation thereof. During operation ofcompressors 24 and 26 compressed refrigerant gas having small amounts ofentrained oil discharges from each of outlets 52 and is conducted viadischarge conduits 58 to the inlet of condenser 14 wherein therefrigerant is cooled and condensed. The refrigerant condensatecontaining small amounts of Inbricating oil passes from the condenseroutlet into receiver 16 from whence it flows to expansion valve 18.Expansion valve 18 throttles the oil containing refrigerant liquid to asubstantially lower pressure into the inlet of evaporator 20. Inevaporator 20' heat absorbed from the conditioned space causes theliquid refrigerant to vaporize. The fiow of vaporized refrigerantsweeping through the evaporator carries the entrained lubrication oilthrough the evaporator outlet into the inlet 62 of connector 60. A majorportion of the entrained oil in the refrigerant entering inlet 62 passeson through outlet 64 of connector 60 for return to compressor 24 viasuction conduit 66. The fact that a major portion of the oil enteringinlet 62 passes out through outlet 64 may be attributed to the flowalignment of the inlet 62 and outlet 64. Suction gas entering inlet 62of connector 60 passes to compressors 24 and 26 via suction conduits 66and 76 respectively. The construction of connector 60 also facilitatesthe maintenance of a higher suction pressure in compressor 24 than incompressor 26. Since a major portion of the oil is returned tocompressor 24, the oil level in sump 46 of compressor 24 will begin toexceed the level permitted by the oil equalizer conduit 54. As the oillevel rises to the inlet of equalizer conduit 54 in compresor 24, oilwill be carried through the equalizer conduit 54 from compressor 24 tocompressor 26 owing to the higher pressure in compressor 24. Bafile 56prevents the refrigerant gas flowin into conduit 54 from carrying anexcessive amount of oil to compressor 26. Should the suction pressuredifferential between compressors 24 and 26 be insufiicient to cause thedesired oil flow from the compressor receiving the major portion of theoil, it may be desirable to slightly crimp or otherwise restrict thesuction conduit of the other compressor as is shown at 72.

Thus it will be seen that the oil return system described herein doesnot require the use of check valves and pumps and does not attempt thedifiicult task of maintaining equal suction pressure on the compressors.The oil return scheme is simple, inherently reliable, and low in cost.This invention has been found to materially increase the reliability ofcompressors arranged in parallel relationship.

Having thus described in detail the preferred embodiment of ourinvention, we contemplate that many changes may be made withoutdeparting from the scope or spirit of our invention and we desire to belimited only by the claims.

We claim:

1. A refrigeration apparatus comprising: a refrigerant condenser means;a refrigerant evaporator means; first conduit means connecting theoutlet of said refrigerant condenser means to the inlet of saidrefrigerant evaporator means; first and second refrigerant compressors;a first oil sump for said first refrigerant compressor; a second oilsump for said second refrigerant compressor; a first suction conduitconnected to the inlet of said first refrigerant compressor and disposedin fluid communication with the outlet of said refrigerant evaporatormeans for conducting refrigerant from said refrigerant evaporator meansto said first refrigerant compressor; a second suction conduit connectedto the inlet of said second refrigerant compressor and disposed in fluidcommunication with the outlet of said refrigerant evaporator means forconducting refrigerant from said refrigerant evaporator means to saidsecond refrigerant compressor; a discharge conduit means connecting theoutlets of said first and sec ond refrigerant compressors to the inletof said refrigerant condenser means for conducting refrigerant from saidfirst and second refrigerant compressors to said refrigerant condensermeans; means for operating said first and second refrigerant compressorssimultaneously; means for maintaining the pressure in said first oilsump higher than the pressure in said second oil sump duringsimultaneous operation of said first and second refrigerant compressors;means for returning a greater portion of any oil entrained in therefrigerant leaving said evaporator means to said first oil sump thansaid second oil sump; and an oil equalizer conduit means separate fromsaid second suction conduit connecting said first oil sump to saidsecond oil sump for conducting excess oil from said first oil sump tosaid second oil sump via the pressure differential between said firstand second oil sumps.

2. The apparatus as defined by claim 1 wherein said means for returninga greater portion of the oil entrained in the refrigerant leaving saidevaporator means to said first compressor includes a three-wayconnection having an inlet connected to the outlet of said refrigerantevaporator means, a first outlet disposed substantially in fluid fiowalignment with said last mentioned inlet and connected to said firstsuction conduit, and a second outlet disposed substantially out of fluidflow alignment with said last mentioned inlet and connected to saidsecond suction conduit whereby oil entrained in refrigerant gas enteringsaid last mentioned inlet tends to be discharged from said three-wayconnection through said first outlet.

3. The apparatus as defined by claim 2 wherein said three-way connectionis generally T-shaped wherein the angle between the inlet thereof andsaid second outlet is acute and the angle between said first and secondoutlets is obtuse.

4. The apparatus as defined by claim 1 wherein said means formaintaining the pressure in said first oil sump higher than the pressurein said second oil sump includes means for rendering said second suctionconduit of greater resistance to fluid flow than said first suctionconduit.

5. The apparatus as defined by claim 4 wherein said means for renderingsaid second suction conduit of greater resistance to fluid flow thatsaid first suction conduit is a discrete flow restrictor disposed withinsaid second suction conduit.

6. The apparatus as defined by claim 5 wherein said discrete flowrestrictor comprises a crimp in the walls of said second suctionconduit.

7. The apparatus as defined by claim 1 wherein said means for returninga greater portion of any oil entrained in the refrigerant leaving saidevaporator means to said first oil sump returns said greater portion ofsaid oil via said first suction conduit.

8. A refrigeration apparatus comprising: a refrigerant condenser means;a refrigerant evaporator means; first conduit means connecting theoutlet of said refrigerant condenser means to the inlet of saidrefrigerant evaporator means; a first hermetically sealed casing; afirst motorcompressor unit resiliently mounted within said first casing;a. second hermetically sealed casing; a second motorcompressor unitresiliently mounted within said second casing; said firstmotor-compressor unit having a suction inlet in fluid communication withthe interior of said first casing and said second motor-compressor unithaving a suction inlet in fluid communication with the interior of saidsecond casing; discharge conduit means extending through each of saidcasings connecting the discharge outlet of each of said first and secondmotor-compressor units to the inlet of said con-denser means; each ofsaid casings defining in the lower portion thereof an oil sump for themotor-compressor unit disposed therein; a first suction conduitconnected to the interior of said first casing and disposed in fluidcommunication with the outlet of said refrigerant evaporator means forconducting refrigerant from said refrigerant evaporator means to saidfirst casing; a second suction conduit connected to the interior of saidsecond casing and disposed in fluid communication with the outlet ofsaid refrigerant evaporator means for conducting refrigerant from saidrefrigerant evaporator means to said second casing; means for operatingsaid first and second motor-compressor units simultaneously; means formaintaining the pressure in said first casing higher than the pressurein said second casing during simultaneous operation of said first andsecond motorcompressor units; means for returning a greater portion ofany oil entrained in the refrigerant leaving said evaporator means tosaid first casing via said first suction conduit than to said secondcasing via said second suction conduit; and an oil equalizer conduitmeans separate from said second suction conduit for conducting excessoil in said first oil sump to said second oil sump via the pressuredifferential between said first and second casings.

9. The apparatus as defined by claim 8 wherein a baffie is disposed insaid first casing adjacent the connection of said oil equalizer conduitto retard the entrainment of oil in the gas passing through said oilequalizer conduit from said first casing to said second casing.

References Cited UNITED STATES PATENTS 2 076,332 4/1937 Zercher 62-468 X2,294,552 9/ 1942 Gygax 625 10 X 2,663,164 12/1953 Kurtz 62-468 ROBERTA. OLEARY, Primary Examiner.

W. E. WAYNER, Assistant Examiner.

